What is a coral, really? It’s an animal, but it is also plantlike, an alien amalgam of many clades. It is made up of minuscule individuals and yet its colonies comprise the largest living structures in the natural world.

Zooming in reveals the tiny components and processes that make up the organism: the fleshy coral polyp within its calcium carbonate skeleton; the microscopic algae that live in symbiosis inside the cells of the animal; the complex microbial communities that live in and around all of them. You’d also observe the way ocean chemistry interacts intimately with the creatures, changing their ability to grow, or the way a half-degree difference in temperature can upset their delicately balanced cellular machinery.

Zooming out to the reefs themselves reveals geological structures reaching up from the seafloor, growing from millions of tiny mouths and built on the compiled skeletons of previous generations. These house fish and sea urchins that graze on the algae that might otherwise overgrow the corals, larger fish that eat them, and species like sharks, whose existence marks a well-balanced ecosystem and whose absence indicates disorder. Other organisms prey on the coral itself: The crown-of-thorns starfish is so fecund and insatiable that a single individual can populate whole square miles of reef, stripping the coral of its polyps and leaving dead, white skeletons behind.

Humans have a way of messing with coral at both ends of the scale, from altering the very chemistry of the water they grow in, to destroying thousands of miles of reef by dredging, polluting, overfishing, and just generally overloading them.

But some people think that in order to fix coral, we’ll have to keep meddling. We’ll just have to do it better.

The Coral Restoration Foundation’s nursery is made up of PVC-pipe “trees” where corals grow quickly in the nutrient-rich current.Coral Restoration Foundation

Ken Nedimyer, founder of the Coral Restoration Foundation, leans hard on the coral-as-trees metaphor. If you can regrow a forest from a nursery, he thought, why not a reef? Aside from a few frustrating particulars and unknowns about coral husbandry, the model made sense to him. But no one had tried it.

In 40 years of diving in the Florida Keys, Nedimyer has watched the place change into something unrecognizable: “The reefs I saw in the early ‘70s were just fabulous. I remember going to Carysfort, and it was just acres and acres of elkhorn coral, coming right to the surface. You couldn’t swim over it; you couldn’t see the end of it. Most of the reefs in the Florida Keys were like that.”

As the stepping-stone islands filled up with people, the surrounding seas filled up with their boats and sewage. Until very recently, wastewater from the Florida Keys was flushed right out to sea or pumped into leaky septic systems. As a result, all those spectacular near-shore reefs that had made the place famous suffered a 30-year-long string of disease outbreaks, algal blooms, dredging, damage from boats, and overfishing. Today, the Carysfort Reef has mostly turned to skeletal rubble, overgrown with algae and largely empty of fish.

The problem with coral in the Keys is not unique in the Caribbean. A comprehensive study of the Caribbean’s reefs from 1972 to 2012 found that coral declined by more than 80 percent, with most of that loss concentrated in the 80s and 90s. An outbreak of White Band Disease knocked out almost all of the region’s staghorn and elkhorn corals — the branching corals that make up the bulk of the region’s reef structure. Another disease wiped out the local sea urchins that kept algae in check. Then in 1997 and 1998, the strongest-ever El Niño observed to-date hit, and ocean temperatures shot up. Caribbean corals, struggling in the hot water, expelled their symbiotic algae and slowly starved to death, in some of the worst bleaching events in the history.

In the late 90’s, a series of papers proclaimed the end of reefs, eventual or imminent. Even if we could stop dumping so much sewage and sludge on the reefs, we almost certainly couldn’t stop the global warming that had already started raising ocean temperatures above the threshold at which coral survival seemed impossible. Surely these fragile creatures, the foundation for so many critical ecosystems, would not be able to exist in that hot future world. Surely, they were all doomed.

But what seemed like a foregone conclusion to pessimistic scientists seemed like a call to arms for others. Nedimyer was of the latter. An aquarium collector, he spent most of his time underwater, catching tropical fish to sell to public and private aquariums. When an elkhorn coral started to grow on some aquarium “live rock” he was tending, Nedimyer had an idea. While elkhorn is a federally protected species in the Caribbean, the law was that anything growing on Ken’s live rock — including elkhorn — belonged to him. He could do what he wanted with it.

Nedimyer knew he could probably make a tidy fortune by growing the rare coral to sell cuttings to aquariums. But he wanted to do something bigger. So Nedimyer and his 13-year-old daughter started with a 4H project, fragmenting the original coral to grow each piece into a new colony. They were practicing for the nursery Nedimyer had pictured, an enormous underwater forest capable of restoring the Caribbean’s reefs to their former state, the way he had known them 40 years before.

A thicket of transplanted staghorn coral takes root in the Florida Keys. Grist | Amelia Urry


In 2003, Nedimyer got federal permission to plant six corals in a spot on Molasses Reef in the Florida Keys. In 2007, after a string of bad luck and hurricanes that kept them off the reef, they planted 18. In 2015, Nedimyer and the small staff of the Coral Restoration Foundation, along with a legion of volunteers, planted more than 18,000 of them.

Jessica Levy manages the CRF’s restoration program, which means she is out on the water most days — gathering corals from the nurseries, monitoring for signs of trouble, and planting new batches of coral on the reef. The corals she works with are the offspring of wild patches of elkhorn and staghorn that survived the mass die-offs of the last few decades.

“If they’ve gone through bleaching events and survived, if they’ve gone through cold events and survived, they’re a stronger coral,” Levy says. “They’re the ones that you want to fragment and grow and plant back on the reef. The idea being, if they survived it then, they’ll survive it now.”

In the nursery, coral grow two or three times faster than they grow on the reef. Suspended in the water column, they can gather nutrients from the current and grow in all directions without expending energy to affix themselves to the reef. Once planted, they spend a few months stabilizing, forming new tissue over the epoxy used to cement them in place. Then they start growing again.

Since they’re planted in groups of the same genotype, the corals grow together as they get bigger, forming tangled thickets that provide the kind of shelter and support a reef so badly needs. Levy says that, so far, about 80 percent of the transplants are still alive after two years on the reef. Impressive results, especially considering no one has ever tried a project like this at scale before.

A volunteer coordinator for CRF readies a boatload of divers.Grist | Amelia Urry


Nevertheless, Nedimyer and Levy and the rest of CRF know they are facing a Herculean task if they expect to replant all of Florida’s reefs by hand. But, luckily, they don’t. Even the reefs where they’ve been planting corals since the beginning are still mostly bare, featuring the odd thicket of staghorn or stubborn boulder coral.

Levy says CRF’s real goal is not to repopulate the reefs coral by coral, but to preserve the genetic diversity the species needs to stay resilient. By gathering corals from the reef, CRF can save genotypes that might otherwise be lost from the wild. Eventually, if CRF can just boost population density a little, the corals can start reproducing on their own again.

“One of the biggest obstacles is that as these populations stand now, when they do go to spawn, they’re so far apart,” Levy points out. Corals are hermaphroditic, producing bundles of both sperm and eggs during a yearly spawning event, but elkhorn and staghorn can’t fertilize themselves. They trust that their spawn will mingle in the water column, meet other coral spawn, fertilize, and avoid being eaten long enough to settle out and start growing new coral. But right now, says Levy, “these guys are so fragmented that there’s no chance of meeting up.”

“It’s a big ocean. The goal was never to outplant every coral on every reef. That’s not sustainable,” Levy says, on a rare day in her office on land. That’s the part that can be hard to explain to people, who can’t see the point of scattering a few thousand corals across reefs that once hosted millions. “The goal is to get genetic diversity out there, to the point where they’re naturally reproducing. Basically, to boost natural recovery.”

If that sounds like a big gamble to you – it is. But it might be our best bet.

To plant a coral, you first have to clear a place for it. You do this (I am a little alarmed to learn) with the chisel end of a hammer.

The day after we gathered our coral cuttings from the nursery, we go out on Molasses Reef, one of the most visited reefs in the Keys. I take a hammer from Patty and tentatively begin tapping the reef substrate, a compressed residue of coral rubble and sand, riddled with strange, iridescent sea worms.

This is not easy. Picture an astronaut trying to hammer a nail in space: For every fraction of an inch the nail goes in, the astronaut floats back a foot. In my case, each careful chisel blow to the rock sends me drifting upward like an untethered balloon. To stay down, I have to direct my head and all my attention downward while kicking steadily, as I scrape the rock clear of its algal fuzz.

I brace my coral firmly against a spot on the cleared substrate with one hand, while with the other I pinch off small globs of purple epoxy. Each branch gets a dab, and the whole thing goes down onto the spot I’ve cleared.

At least in theory: Between my own drift and wafting clouds of sediment from the divers chiseling on either side of me, it takes some maneuvering before I can get my branch of staghorn anchored firmly to the rock. To test its structural integrity, I wave my hand over it like I’m trying to fan out a flame. Sediment flies up in a cloud, but my coral — it stays put. Success.

It takes about 40 minutes for four of us to plant all 10 corals in one thicket, an area easily encompassed by a hula-hoop. As all the groups start to ascend, I can’t help but think that it doesn’t look like much. Together, we have managed to plant a single milk-crate’s worth of corals over a badminton court-sized patch of seafloor. This on the bare, rocky remains of a reef that stretches to the limits of visibility.

But something happens as we continue to rise. Fish dart in to fill the space we have made, rushing to gulp the worms we’ve dislodged in all that scraping and hammering. Suddenly, our sad jumble of coral looks a lot more like a habitat.

From 20 feet above the sea floor, I can see thickets of staghorn planted in the previous year or so. I can see how the disparate pieces of coral have grown up and together, knitting their branches into a kind of a dome. I can see, finally, where they have grown over the epoxy lumps that first sealed them to the reef. They have already taken root.


Continue to Part 2: Selection